What Is an Aquifer Test?

An aquifer test is a process used to examine the hydraulic properties of groundwater sources. These tests are general performed by hydrologists, who study the movement and distribution of water above and below the earth's surface. An aquifer test can help these scientists determine the best place to drill a new well, or allow them to test water quality within a specific region.

Aquifers include all water-bearing regions below the soil. Groundwater is naturally occurring in soil at all times, but the amount of groundwater and man's ability to access it can vary widely. Groundwater distribution depends on factors like soil composition, rain levels, and natural water sources within the area. An aquifer test can reveal whether water is plentiful below the ground, like in sandy soil, or in low supply, like in an area of solid rock.

The simplest aquifer test method involves pumping water out of the aquifer at a constant rate for an extended period of time. These tests are generally performed for at least a day, but may go on for much longer. As the water is pumped from the aquifer, the hydrologists measures pressure changes as well as changes in hydraulic head, or drawdown. This is a measure of the distance between the top of the water supply and the surface of the earth.

Once the aquifer test is complete, scientists typically analyze results using the Theis method, which is named after a United States Geological Survey (USGS) scientist. Theis developed the statistical test methods that still serve as the benchmark for most aquifer testing methods today. The Theis method assumes a non-leaky aquifer with an infinite supply of water, but has been modified to fit other conditions as well.

Hydrologists can gain a great deal of information from an aquifer test combined with this type of analysis. They can find the conductivity, or flow rate of the aquifer under constant pressure. They can also calculate yield, which represents the total water content of the aquifer. Finally, an aquifer test may reveal the size and scope of any leaks, as well as the total size and boundaries of the aquifer.

An aquifer test is one of the most effective methods for determining the best location to drill a new water well. Rather than waste time and money with exploratory drilling, the aquifer test can help work crews find large water supplies as quickly as possible. These tests also play an important role in pollution control, and can help scientists discover the concentration of contaminants in a particular location.